Keying devices, particularly for electrical musical instruments



Aug. 31, 1965 A. MICHEL 3,204,177

KEYING DEVICES, PARTICULARLY FOR ELECTRICAL MUSICAL INSTRUMENTS Filed Nov. 2, 1961 'INVENTOR: W fiZJc/Z United States Patent 3,204,177 KEYING DEVICES, PARTICULARLY FOR ELEC- TRICAL MUSICAL INSTRUMENTS Adolf Michel, Dietramszellerstrasse 2, Munich 25, Germany Filed Nov. 2, 1961, Ser. No. 149,736 2 Claims. (Cl. 323-56) In the function of an electronic musical instrument, keying devices are required to switch a large number of available tone sources to a common amplifier when the corresponding keys are actuated by a player.

The simplest form of keying is an electrical contact. Formerly used exclusively, today still frequently used, such contacts have the drawback that they cause a phasedependent key click; i.e., the click is maximum if the contact is closed when the instantaneous current amplitude is maximum; it is zero if the contact is closed at the instant the current is going through zero.

FIGURE 1 shows a touch responsive musical keying device; 7 FIGURE 2 illustrates a plurality of the devices of FIG- URE l;

. FIGURES 3, 4 and 5 show modifications of the device of FIGURE 1;

FIGURES 6-10 disclose further modifications of the keying device employing toroid core elements.

In instruments of more advanced developments, devices are found whose operation is based on a second switching circuit, that either switches the oscillator themselves; or arrangements are used in which a controlling rectifier in each audio supply lead is opened via an R-C coupling circuit; or also a charge is applied to a condenser via each R-C circuit, whose capacity varies synchronously with the simultaneous audio oscillation. Here the key click is really eliminated, and the oscillation build-up of the keyed audio frequency follows an exactly prescribed function (usually an e-function), although this renders certain musical interpretations impossible (as, for instance, change from legato to staccato) during the playing. Besides, the number of parts required for building such a circuit is excessive. The ideal system is a touch responsive keying system, which faithfully follows the interpretation of the player. The most sophisticated result of efforts in this direction is of course the magnetic bridge with a safety contact, as described in French Patent No. 929,578. This consists (per FIGURE 1) of a primary coil A, a secondary coil B, and a compensating coil C, along with an iron core D which is coupled (mechanically) to the key as well as to contact E. Coil A is connected to audio oscillator T; coil (coils) B is (are) connected to amplifier V; coil C compensates for the voltage induced in coil B from A at the moment contact E is closed. In this way, a clickless introduction of the tone frequency is possible, and its envelope is also responsive to the players touch.

FIG. 2 shows the interconnection of several keying circuits of the type shown in FIGURE 1, in one keyboard assembly. Here it is evident that because of the series connection of coils B1 through Bn the output impedance is increased by a factor K (K=the number of keying circuits); i.e., the audio power available at the input of the amplifier therefore is the power of the several circuits divided by the same factor K, providing that the E.M.F.s of all the coils B are equal, and that the matching is perfect. If an arrangement of parallel connected coils B is considered instead, the same result will be reached.

If now a homogeneous external noise field is assumed, which affects all coils B equally, the noise power fed to the input of the amplifier will also increase by the factor K, from which it is evident that the signal to noise Patented Aug. 31, 1965 "ice ratio will be a function of the factor K This means that with a normal keyboard of 50 keys the value of the factor K will be 2500. This becomes particularly critical if the output of the audio oscillators is low.

The principal object of this invention is to improve the keying system whose principles are described above, so that with relatively small output power from the oscillators T1 through Tn, a suflicient amount of input power will be provided to the following amplifier V. This invention proposes that the problem will be solved by simultaneously and continuously changing the impedance of coils B while changing the coupling.

The following will better illustrate the invention by means of some practical examples:

The arrangement of FIGURE 3 differs from FIGURE 1 by the addition of an adjacent core F, which is fastened to core D by an intermediate member Z and positioned within coils B and C when at rest. In contradistinction to core D, core F is made of nonmagnetic but electrically conductive material, and in the nonactuated position of the key it decreases the impedance of coil B (by acting as a shorted turn). Upon pushing the key, shorting core F is pushed out of coils B and C, and mag netic core D establishes coupling between coils A and B in the usual manner.

Two further examples of the invention are given in FIGURES 4 and 5. Here the change of, coupling and impedance is accomplished by magnetically saturating the stationary core D (for instance a ferrite core) with a steady magnetic field from a permanent magnet NS fastened to the key. Magnet NS is close to the core D when the-key is released. Here a change of impedance by a factor of 20 to 30 can be practically realized, and compensating coil C can be eliminated, since the switching transient is reduced by the same factor of 20 to 30. The example shown in FIGURE 5 differs from that in FIG- URE 4 by the addition of a step in cross-sectional area of the core D, so that the portion of the core in coil B is smaller, by which saturation occurs only for coil B, and the decoupling resistor R shown in FIGURE 4 can be eliminated.

FIGURE 6 shows a (ferrite) toroid used as a transfer element with which significantly fewer turns are needed because of high permeability. Coils A and B are wound on this toroid. By making use of a toroid of varying cross sectional area (as that shown in FIGURE 7, for instance) saturation by the permanent magnet field in the thinner sections where coils A and B are wound can be increased, and thereby a greater ratio of signal transfer can be achieved.

Any magnetic external noise field influence, which is inevitably present to some extent at least, can be compensated for in a toroid core by distributing the winding B evenly around the core, or at least dividing it into two diametrically located windings. By so doing, the direction of winding on opposite sides of the core is in opposite directions. Thus any stray magnetic field, such as indicated by the arrows in FIG. 8, will influence the portions of the coil on the two sides of the toroid oppositely so that the current induced at one side is cancelled by the current induced at the opposite side.

In the structure of FIG. 9 the permanent magnet NS, illustrated in the previous embodiments, has been omitted, and in its stead an electromagnetic coil EM has been used. DC current in this coil is controlled by normally closed key contacts K which normally maintain the coil current until the key is depressed. At this juncture, contacts K are interrupted and contacts E are made which control the current from the generator T in the coil A as in the previous embodiments. The core through the coils A and B is therefore kept saturated by the electromagnet E, except when the playing key is depressed. The ultimate result, therefore, is much the same as that produced by the previous arrangements, such as that of FIG. 4 for instance. If in a particular instance the magnetic field produced by the coil EM builds up or dies out too rapidly, a shorted turn may be used in a well known manner about the core to delay the rate of magnetic flux change.

An advantageous modification of the arrangement of FIG. 9 is illustrated in FIG. 10. Here two toroids X and Y are illustrated together in edge-to-edge relationship. The control winding ST, which is the equivalent of EM of FIG. 9, is wound around both of the toroids where they are together so that when this winding is energized by a keyed DC. current, both toroids are saturated. The primary winding A and the secondary winding B are then wound half on one toroid and half on the other, with both halves wound in the same direction so that the transient magnetic field produced by keying the DC. circuit will have a cancelling effect in the two halves of the windings of both the primary and the secondary. This arrangement eliminates the transient efr'ect normally caused by keying. Keying is accomplished simply by interrupting the DC. circuit through the coil ST in the same way that contacts K of FIG. 9 interrupt the current through coil EM. It will be appreciated that this controlled coupling system can be used in devices other than electrical musical instrument keying circuits. It should be noted that it acts as a controllable coupling device without requiring the use of contacts in either the primary or secondary, since the coupling between the primary A and the secondary B can be established or interrupted simply by removing or establishing a current through the winding ST.

Having described my invention in conjunction with several illustrative embodiments thereof, which will suggest variations within the scope of the invention, what I 1 claim as new and useful and desire to secure by Letters Patent is:

1. A device for varying the coupling between an input and an output circuit comprising a pair of toroidal cores in close tangential juxtaposition with their axes subtantially parallel, a control coil wound around both of said cores where they are in juxtaposition, a primary coil wound partly on one of said cores and partly on the other of said cores, a secondary coil wound partly on one of said cores and partly on the other of said cores, the two parts of said primary being wound in the same direction and the two parts of said secondary being wound in the same direction, and circuit means including a key for varying the current density in said control coil to vary the degree of saturation of said cores, said cores being of the signal type for transmitting musical signals, the said transmission depending on a continual change of permeability which results in the change of the amplitudes of the signals, said last-named means including contacts normally closed and means for breaking said contacts by means of said key.

2. The invention as defined in claim 1, wherein said circuit means includes a battery.

References Cited by the Examiner UNITED STATES PATENTS 1,287,982 12/18 Hartley 336229 X 2,218,711 10/40 Hubbard 32356 2,467,807 4/49 Camilli et al 323-83 X 2,939,019 5/60 Ridler et a1 323-89 X 2,975,298 3/61 Fawcett et al. 32389 X LLOYD MCCOLLUM, Primary Examiner. ROBERT L. SIMS, Examiner. 

1. A DEVICE FOR VARYING THE COUPLING BETWEEN AN INPUT AND AN OUTPUT CIRCUIT COMPRISING A PAIR OF TOROIDAL CORES IN CLOSE TANGENTIAL JUXTAPOSITION WITH THEIR AXES SUBTANTIALLY PARALLEL, A CONTROL COIL WOUND AROUND BOTH OF SAID CORES WHERE THEY ARE IN JUXTAPOSITION, A PRIMARY COIL WOUND PARTLY ON ONE OF SAID CORES AND PARTLY ON THE OTHER OF SAID CORES, A SECONDARY COIL WOUND PARTLY ON ONE OF SAID CORES AND PARTLY ON THE OTHER OF SAID CORES, THE TWO PARTS OF SAID PRIMARY BEING WOUND IN THE SAME DIRECTION AND TWO PARTS OF SAID SECONDARY BEING WOUND IN THE SAME DIRECTION, AND CIRCUIT MEANS INCLUDING A KEY FOR VARYING THE CURRENT DENSITY IN SAID CONTROL COIL TO VARY THE DEGREE OF SATURATION OF SAID CORES, SAID CORES BEING OF THE SIGNAL TYPE FOR TRANSMITTING MUSICAL SIGNALS, THE SAID TRANSMISSION DEPENDING ON A CONTGINUAL CHANGE OF PERMEABILITY WHICH RESULTS IN THE CHANGE OF THE AMPLITUDES OF THE SIGNALS, SAID LAST-NAMED MEANS INCLUDING CONTACTS NORMALLY CLOSED AND MEANS FOR FOR BREAKING SAID CONTACTS BY MEANS OF SAID KEY. 